Microphone



July 30, 1929. B. F. MIESSNER I ,7

MICROPHONE Filed May 14, 1925 INVENTOR Benjamin F/i/Aessner ATTORN EY6 Patented July 30, 1929.

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BENJAMIN I. MIEfiSNEB, 01 SOUTH OBAJVGIE,

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MICROPHONE.

Application am May 14, 1925. serial No. 30,164.

5 ing purposes.

It is the ob'ect of this invention to pro- I vide a microp one pickup which is exceedingly sensitive and approximately equally sensitive to sound waves propagated from all sides. A microphone pickup having these characteristics is especially desirable for use in broadcasting orchestral and other musical group performances, where it is necessary or convenient to place the pickup in the center of a group of musicians or to so place the musicians that the sound waves from the various instruments would not all be conveyed in one or two general directions to the pickup.

Microphone pickups of the kind commonly used, heretofore, are very much more sensi-' tive to sound waves propagated directly against the diaphragm, or diaphragms, than to those propagated along planes parallel and approximately parallel to the p ane of the diaphragm. On this account the best results are not attainable with such pickups in broadcasting the performances of large symphony orchestras and choirs.

A microphone pickup constructed in accordance with the preferred embodiment of "the present invention is illustrated in the accompanying drawings and consists, of a block or sheet ofsponge rubber or other substance having substantially equal resiliency and damping characteristics. An aperture is formed extending through the sheet of sponge rubber and is enclosed at each end by means of exceedingl light, but rigid discs or diaphragms pre erably of mica an each provided with a very thin coating of platinum or other suitable foil on the sides adjacent the sponge rubber sheet. The chamber formed in the sponge rubber sheet by the discs or diaphragm is referably filled with granular carbon whic contacts with coatings of foil and across which the microphone current fiows. The combination of elements thus brought togpthenmay be and is preferably of very lig t Wei ht and is almost equally sensitive to soun waves from all directions.

In the accompanying drawmg,

Fig. 1 is an elevational view of a microcastwhich may be phone pickup, in accordance with this invention and of the preferred form, and,

Fig. 2 IS a longitudinal cross-section thereof.

The microphone pickup illustrated in the drawing, representative of the preferred embodiment of the invention, comprises a molded slab or sheet of sponge rubber 1, about one and one-quarter nches long, one inch wide and one-ei hth nch thick, An aperture 2 about onealf mob in diameter may be formed in the process of molding, the sheet of sponge rubber. A pair of discs or d1aphragms, each comprising a relatively rigid sheet of mica, 3 and 4, respectively, and a thin coatlng of platinum or other suitable foil, 5 and 6, are secured to either side of the sponge rubber sheet 1 and preferably cemented thereto. The platinum foil is also preferably cemented to the mica discs. The chamber thus formed between the two platmum coated discs is partly filled with granular carbon 7. A pair of lead-in conductors 8 and 9 are connected respectively to the two platlnum foil coatings and may, for convenience, be imbedded in the sponge rubber as indicated in Fig. 2.

The principle of operation of this microphone pickup is not unlike that of any other carbon microphone, except that due to the resiliency of the sponge rubber sheet 1 and the small mass of the discs or diaphragms, the device is found to be extremely sensitive .and almost equally sensitive to sound waves or may be cut through rarefaction of the air caused by sound waves effects edge-wise compression and extension of the sponge rubber sheet, thereby varying thepressure of the carbon granules.

The present invention is amenable to con- 1 siderable modification within its scope and spirit and should not be construed as limited except as indicated by the appended claims.

What is claimed is:

1. A microphone comprising a member of hly resilient substance, forming a sound lecting surface having an a rture therein adjacent one ed e of said sul is t-ance, a pair of light, rigid discs attached respectively to o posite sides of said member and forming c osures for said aperture, conducting wires leading from each of said disks through said substance and forming suspension means for freely supporting said substance at a point adjacent the opposite edge thereof and granular micro honic material within the chamber form by said aperture and said discs whereby sound vibrations incident upon said member impart corresponding compressional forces to said granular microphonic material within said chamber.

2. A micro hone comprising a sponge rubber member orming a sound collecting surface having an aperture extending therethrough and unequally spaced from opposite edges of said member, a pair of discs secured to opposite sides-of said member and f0rming closures for said aperture, said discs each comprising a relatively rigid sheet of mica and metallic foil coatings secured to said' discs respectively, said coatings being adjacent said a rture and wire members connected to eacli of'said metallic foil coatings and extending through said sponge rubber member and forming suspension means for freely suspending said microphone and granular carbon partially filling the chamber formed by said aperture and said discs said granular carbon contacting with said metallic'foil coating whereby sound vibrations inci'dent upon said member operate to produce corresponding compressional forces in said granular carbon in saidchamber.

3. A microphone comprising a sheet of sponge rubber having an aperture therethrough, a pair of mica discs secured respectively to opposite sides of said sheet, said discs forming closures for ends of said aper-. ture, respectively, a platinum foil coating on each of said discs, said coatings being adjacent said aperture, the chamber formed by said discs and aperture being partially filled with granular carbon, and lead-in conductors connected respectively to said platinum foil coatings, said sheet of sponge rubber forming a surface against which sound vibrations directly impinge for imparting corresponding compressional forces granular carbon.

In testimony whereof I aflix my signature.

BENJAMIN F. MIESSNER.

to said chamber of 

